Typical asphalt-based roofing shingles include a roofing mat coated with asphalt and covered with a layer of roofing granules. The shingles include a buttlap portion that is exposed when the shingles are installed on a roof and a headlap portion that is covered by the upper adjacent course of shingles when the shingles are installed on a roof. Laminated roofing shingles also include an overlay made from a second asphalt-coated mat on the buttlap portion of the shingles.
U.S. Pat. No. 6,990,779 B2 to Kiik et al. (Elk Premium Building Products) discloses a roofing system having alternating courses of roofing shingles and interply material. The roofing shingles are constructed to have a wider buttlap portion and a narrower headlap portion. The interply material can be comprised of a substrate having an ionic charge coated on both sides with a coating having essentially the same ionic charge, and a water impermeable plastic film or metal foil on one or both sides of the coated substrate. A roofing shingle is commercially available from Elk in which a sheet of interply material is attached to the headlap portion of the shingle.
The following patents disclose metal or plastic sheets attached to the buttlap portions of roofing shingles: U.S. Pat. Nos. 1,655,222; 1,799,500; 2,847,948; 3,377,762; and 3,468,092.